It is known in mobile telephone technology to test the function of mobile telephone units, both during their manufacturing phase and when the units are operational. For instance, it is known to test the function of a mobile unit during its manufacturing phase with the aid of external measuring equipment. Since this type of testing requires the use of heavy and often permanently installed measuring equipment, the method cannot be applied when the mobile unit is operational.
The U.S. Pat. No. 4,554,410, for instance, teaches a method of testing an operational mobile unit, by manually activating a test program. A self-testing program can be activated in the mobile unit by depressing a key on the unit. Different tests can be run, depending on which key is depressed. According to the patent, the result of an executed self-test program can be displayed on the mobile unit. One drawback with this type of test is that it requires the presence of a user or of some other person, for instance a service technician. Since activation of the test requires the presence of a person, the mobile is often tested less frequently than would otherwise be desirable. Neither is the user always aware of the most favourable occasion for activating a test, i.e. an occasion in which the most relevant and optimal result can be obtained. Another drawback with the solution presented in the U.S. patent is that the test is only activated in the mobile unit when the user suspects that the mobile is faulty or at error. However, the most critical errors in a mobile unit are often caused by interference in the surroundings, a fact of which the user is normally unaware. For instance, it is possible that a mobile station does not release itself when a call has been terminated, or that a mobile in a TDMA system transmits on non-allocated frequencies or transmits in wrong time slots. Operators have traditionally contended with these faults and errors with the aid of direction-finding vehicles which localize interfering mobile stations. Localization of interfering mobile stations is both complicated and expensive.
It is also known from Ericsson's published product description of subscriber line testing described in SULTRC 1551-cnt2161293, SULTR 1551-cnt2161294 and SULTD 1551-cnt2161328 a procedure in which a subscriber line and terminal is tested with a starting point from a telephone switching centre or exchange subsequent to the release of a wire-bound call. However, this test requires a test initiating device to be positioned centrally in the switching centre, or exchange.
It is also known that personal computers carry out time-consuming self-test procedures when started up. However, such testing procedures cannot be applied with mobile telephones, since it is unacceptable to a user of a mobile telephone that he/she should wait for a self-test to be run in conjunction with establishing a call connection, the setting-up of which connection is often ordered immediately after the mobile has dialled a telephone number.